Note: Credit to @Truffles and @Justin_Case001 for my review.

Am I interested in talking about this episode? No.

I'D RATHER SIIIIIIIIIIIIIIIIIIIIING!

For Season 8, Nicole Dubuc brought in a few writers: Brian Hohlfeld, Kaita Mpambara, and Kim Beyer-Johnson. Minus Kaita, each of them have strong connections with Dubuc and worked with her on Transformers: Rescue Bots. Gregory Bonsingore is no exception. But for him, he's a little different compared to the rest. Bonsignore is an award-winning playwright and lyricist: His Off-Broadway play "Gorgonzola: A Cautionary Sicilian Tale" won several awards at a Miami musical festival, including Best Musical and Best Music/Lyrics. So to have an accomplished writer on FIM is a treat regardless of outcome.

In his Friendship Is Magic debut, he displays his credentials.

This episode covers a lot of information, comparable to Lost Mark or even MMC. But what he does so well is manage it. How? When scenes weren't as important (i.e., the Map calling), little time's used, but when he needs to delve into the important plot points (i.e., communicating with the kirin, finding Autumn, figuring out what caused the vow of silence), he takes advantage. Therefore, despite an abrupt ending, the story flows well. It goes by fast without rushing through.

As what Twilight said, this is the first time a set of ponies took part in a second quest, this being AJ and FS. And here, each of them were tremendous. Was Fluttershy scared? Thanks to its ominous name and craggy exterior, more than plausible. The Friendship Express quickly hightailing from its weathered station further and freaky clerk support her fear. But as the episode progressed, her fear starts to ease, starting with helping nearby squirrels gather up bright yellow-to-blue flowers, who in return helped her locate the Peaks's real entrance and their discovery of the kirin.

Needless to say, the kirin are gorgeous! Their earthly tones complement really well with their environment and contrast really nicely to the pastel-ly look of AJ and FS. Their manes, horns, toes, tails, and dragon-scale-esque backs are wonderfully designed, with only their brilliant eyes to pop out. And, yes, @Justin_Case001 is right. The tilting of the head makes them look really cute!

But the outsider of the clan, Autumn Blaze, is easily the star of the show and takes up the bulk of the run time compared to the others. Pinkie and Silverstream are massive chatterboxes, but Autumn gives them a massive run for their money. She talks a lot and is full of quirks with solid reason. Other than the view and makeshift toys, she hasn't talked to anyone in ages to the point of forgetting or mispronouncing words. AJ is her first companion since Rain Shine exiled her. And her rapid, sometimes flowery, talk is completely hilarious. Her personality is more than charming. It's warm, bright, and optimistic. Even when she's bored, she finds ways to remain eccentric and hopeful to reunite with her clan, evident in many ways, including her gossip with a stick.

Oh, and We're Friendship-Bound? You're dethroned! A Kirin Tale is the best song of the season. Nuff said!

Not enough? Well, alright. The events Blaze described are quite serious, but because she and the song sound so happy with a boatload of humor (including pop culture jokes referencing Citizen Kane, Hamilton, and especially Phantom of the Opera!), the tone's nowhere nearly that dark. The song itself, written by Big Jim and Dubuc, is really funny with many fantastic lyrics. The kirin society's closed off from outside contact and, if going by the ancient shield Rockhoof used, lived closed off for millennia. Its vow of silence is relatively new in their history, but painted on a nearby rock (and shown to FS offscreen) to remind them of why they accepted this vow.

The graphic imagery in itself paints a really dark era of what happened and, to echo what @Truffles stated in his replies, why Rain Shine (the kirin's longtime empress) was completely justified to take such a drastic measure in the first place. The kirin clan devolved into a literal flame war over who'll buy a homemade water pitcher, and their nirik fight destroyed their water supply, flora, and village. But even after becoming homeless, they kept going, and some of them were completely incapable of controlling their temper, hence their sustained nirik form. Had Rain Shine not step in and order everyone to step into the Stream of Silence and suppress their feelings, they'd lose more than just their village, but way of life or even themselves. And in response to those who criticize Rain Shine's plan as flawed, that's the point. Anger's normal, and it's okay to express your anger. But it's important to channel it responsibly. Rain Shine's solution restored order and peace within the Peaks of Peril, but sacrificed being able to communicate and feel without being reminded of why they suppressed their emotions. The following lyrics metaphorize the very moral:

1. Rainbows won't light up the sky unless you let it rain.
2. Shiny apples sometimes come with worms.
3. Candles just won't glow until they burned.

And that was why the Map called AJ and FS: to teach them how to constructively moderate their anger and disagree without sacrificing their joy, ability to feel, or fearing to hurt each other's feelings and reunite Autumn with the others.

Why Applejack and Fluttershy in particular? For a few reasons.

1. Applejack can tell the firm truth while also being sensitive to their feelings. She's not afraid to express what went wrong or what goes against her core morale without marginalizing them. In short, she tells the truth because she cares. If you have someone like Starlight, you run the risk of undercutting the very moral you're trying to teach, because she's plain and blunt, and with a history as sensitive as the kirin's, even more so. AJ's softer personality balances out better with the conflict as well as Fluttershy's further tenderness and care for the animals who live with them.
2. Fluttershy is way more connected to the animals than anyone else. When they're happy, she's happy, and when they're sad, she's sad. She understands what they want, how they feel, and what they're saying. She inadvertently discovered leftover Foal's Breath flowers for the squirrels, and in return, they help them discover the Peaks' true entrance. Because of her ability to read emotions and understand what's wrong, she's observant in how to properly communicate with the kirin, including advising Applejack to ask yes or no question (even though AJ contrivedly ignored that to begin Act 2 ). Despite being initially frightened, she grew more comfortable around them as AJ searched for Autumn Blaze. Observe how she stopped being scared after Applejack returned to the village.
3. The episode validates both their arguments, which won't work with another pair. Autumn's explanation packs the events with a lot of humor, which masked its seriousness. But because the kirin are mute and emotionally suppressed, Fluttershy fully realized how serious the situation was immediately. Her closeness to the wilderness justifies her to opt for the opposite solution. OTOH, AJ had a valid argument, too, which was find the Foal's Breath flower to free them from their vow of silence so they can emote and communicate again. Both sides have a point, rounding the conflict. It's easy to see why they briefly argued; they were both passionate about solving the kirin dilemma and couldn't find common ground, which they did after Blaze rescued them and used her anger and nirik alter ego to protect them from harm.

And @Justin_Case001 makes three great points in his review.

1. This is an episode about communication, more specifically being able to communicate without fear of hurting each others' feelings or starting an argument. Is it important to be sensitive to others? Without a doubt. Otherwise, you suggest you don't care. But it's important to talk to people, communicate with them, and find common ground to compromise without compromising your integrity. While The Cutie Map is about being diverse in your opinions, talents, and personalities, Sounds of Silence is about being diverse in how to communicate and find common ground.
2. As I mentioned before, anger is important and will always be a part of your life. Unfortunately, it's attached to many harmful stereotypes, i.e., the angry black woman, which stigmatizes the emotion. But in itself, it's okay to be angry. Just like anger in itself is important, constructively channeling it is even more important. The nirik's temper were out of control, and until the end, only Autumn Blaze figured out how to manage it without manifesting into something worse.
3. Fluttershy's solution to the friendship problem — keeping the kirin silent — is the wrong option, and she realizes it after they nearly dunked them into the Stream of Silence. However, it's very clear she didn't come to this conclusion with the worst intentions, but instead the opposite. Fire and wood mix easily, and nature is vital to the health of the kirin's secluded village and society. The nirik's temper was clearly a traumatizing event that she and the village altogether don't want to repeat, and this extreme option seemed to be the best one. Observe their faces as they argued:
   
   They were clearly distressed. Their heated argument reminded them of what happened long ago. That's why they interrupted it before it escalated.

Other than the pacing, cramming of detail, and AJ getting briefly nailed with the stupid stick, its last flaw is how obvious the Foal's Breath flower's impact into solving the friendship problem becomes as the plot progresses. Fluttershy and the story spent a good amount of time arranging it for the squirrels, and its brilliant gradients of blue to yellow with all that detail stand out really strongly against the dirty-looking desert. The fact that Blaze landed in a bed of identical flowers and made a tea out of them connects the dots much more.

Yet, they're all very minuscule in the thick of things. Bonsignore's scripting talents really shine with well-done dialogue, pleasant characterization of AJ, FS, and Autumn Blaze, and intelligently simple story. Despite its fast pacing, the script is tight and polished; everything logically flows from one point to another without anything out of place. Since S4, FIM plugs in one episode featuring at least one celebrity guest: Weird Al for Pinkie Pride, Lena Hall for Mane Attraction, Patton Oswalt for Stranger Than Fan Fiction, Felicia Day & William Shatner for The Perfect Pear, and now Rachel Bloom (Autumn's VA) for this one. DHX, now Allspark Studios, puts forth a ton of effort into making the guests belong into the story, and that hard work pays off into an excellent episode (with TPP museum-worthy). Sounds of Silence is no exception. In an already-phenomenal Season 8, this is another addition to the pile of outstanding episodes.